Organic electronic elements are elements which perform electrical actions using organic matter. It is expected that organic electronic elements will be able to provide advantages such as energy conservation, low prices and superior flexibility, and they are attracting considerable attention as an alternative technology to conventional inorganic semiconductors based mainly on silicon.
Among organic electronic elements, organic EL elements are attracting attention, for example, as substitutes for incandescent lamps or gas-filled lamps in large-surface area solid state light source applications. Further, they are also attracting attention as the self-luminous display most likely to replace liquid crystal displays (LCD) in the field of flat panel displays (FPD), and commercialization of organic EL elements continues to progress.
Organic EL elements are broadly classified into two types depending on the organic material used, namely low-molecular weight organic EL elements and polymer organic EL elements. Low-molecular weight materials are used as the organic material for low-molecular weight organic EL elements, and polymer materials are used as the organic material for polymer organic EL elements. Compared with low-molecular weight organic EL elements, for which film formation is mainly performed in a vacuum system, polymer organic EL elements can employ simple film formation methods such as printing or inkjet application. Accordingly, it is expected that polymer organic EL elements will be indispensible elements for future large-screen organic EL displays.
Both low-molecular weight organic EL elements and polymer organic EL elements have already been researched intensively, but improving properties of the elements such as the luminous efficiency and the lifetime of the element remain problems. Using multiple layers for the organic layer that constitutes the organic EL element is used as one method of addressing these problems.
In a low-molecular weight organic EL element, because film formation is generally performed by a vapor deposition method, multilayering can be easily achieved by sequentially changing the compound used in the vapor deposition. On the other hand, multilayering is problematic in polymer organic EL elements. The reason for this problem is that, in polymer organic EL elements, because film formation is performed by a wet process such as printing or inkjet application, the previously formed lower layer dissolves during formation of the upper layer. In order to enable multilayering of a polymer organic EL element, a method is required in which the already formed lower layer does not change during formation of the upper layer.
In order to achieve multilayering, investigations have been conducted into the use of compounds having significantly different solubility levels. One typical example of this method is an element having a 2-layer structure consisting of a hole injection layer composed of polythiophene:polystyrene sulfonic acid (PEDOT:PSS) formed using a water dispersion, and a light-emitting layer formed using an aromatic organic solvent such as toluene. In this case, because the hole injection layer composed of PEDOT:PSS does not dissolve in the aromatic organic solvent, the 2-layer structure can be produced.
However, in this element, the removal of water is problematic, and water can cause a deterioration in the properties of the organic EL element. Further, because drying at a high temperature and/or for a long period of time is performed to remove the water, preparation of an organic EL element using a resin substrate is difficult. Furthermore, there are considerable limitations associated with processes in which reduced pressure conditions are required for the removal of water.
Another method for achieving multilayering that is being investigated utilizes reactions between compounds (for example, see Non-Patent Document 1, Patent Document 1, and Patent Document 2). These documents disclose methods of achieving multilayering by reacting a polymerizable substituent that has been introduced into a compound. For example, these methods include multilayering that uses the polymerization reaction of a silyl group, styryl group, oxetane group or acrylic group or the like, and multilayering that uses the dimerization of a trifluorovinyl ether group or a benzocyclobutene group or the like.